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Aviation History
1929
1929 - 1214.PDF
FLIGHT, JUNE 13, 1929 SINGLE-SPAR MONOPLANE WINGS Details of the Stieger Mono-Spar System Revealed • FOR several months now rumour has been busy concern-ing a new form of wing construction, which wasalleged to have " revolutionised " aircraft construc- tion, and at the same time to have solved all the problemshitherto met with in the production of monoplane wings, more particularly cantilever monoplane wings. Let it besaid that the originators of the new system make no such strong claims, but were somewhat handicapped in the matterof explanations by restrictions connected with patents, &c. These restrictions have now been overcome, and it has be-come possible to give an outline of at least one form which the new type of wing construction may take. Before describing the Stieger mono-spar wing system, itmay be of interest to recall that, with the exception of Mr. Stieger himself, those interested in the development ofthe new wing system are all well known in British aviation the Air Ministry test figures, and thus it may be possible laterto form a clearer opinion of the merits of the Stieger system. In the meantime, the figures quoted are such as to causeone to regard the new type of construction with more than ordinary interest. Our diagrammatic sketch shows one form which jtheStieger wing may take : the single spar -is shown as an I-section beam, but we take it that it could actually bealmost any section desired, such as a box or a lattice girder beam. The I-section is good in bending, but not of muchuse in torsion, and it is presumed that there would be no objection to using other sections. The basic idea of Mr. Stieger's invention consists in usinga single rigid member, completing the structure entirely with tension members, i.e., wires, tie rods, cable or the like. In the Stieger single-spar wing, the only compressioncircles. Mr. Stieger is, ws understand, a Swiss engineer, and member is the spar itself, the rest of the structure being MAIN SPAR was employed in Beardmore's aircraft department. Whenthat closed down, he with Mr. Alan Chorlton and Squadron- Leader Rollo Haig, also of Beardmore's, formed, withMr, M. L. Bramson, of anti-stall gear fame, the Mono- spar Co., Ltd., for the development and exploitation of thenew wing system. The address of the new company is at 4, Broad Street Place, London, E.C.2. In itself the single-spar wing is no novelty. In Germanylarge numbers of gliders have been built hav- ing but a single main spar, and more recentlysuch German aircraft firms as the Bavarian Aircraft Works (B.F.W.), whose designer isHerr Messerschmitt, have produced commer- cial aircraft in which the wings have singlespars, built of metal. German practice is to use a main I-section or box section, and tocover the leading edge of the wing also with plywood or metal as the case may be, thusbuilding up a tube composed of a curved front wall and a straight rear wall, the com-bined spar and leading edge forming a letter D in section. In this country also we havehad single-spar monoplane wings, such as, to take one example which comes to mind, thetriangular box section spar designed by Mr. H. S. Shackleton for the little A.N.E.C. mono-plane. In all these cases the first aim of the designers has been to produce a spar whichnot only resists pure bending load without too pronounced deflection, but also torsionalloads caused by travel of the c.p., and use of ailerons. Of the two problems the formeris probably far the easier, and the latter, i.e., that of avoiding torsion, is aggravated by the ever-present fear of flutter. In this country the cantilever monoplane wing has neverbecome really popular, and not the least reason for that has doubtless been the fear of torsion and flutter. Highly-qualified technicians are still divided on the question mono- plane or biplane, and the pros and cons have been advancedby both schools with about equal strength, so that so far no theoretical basis exists upon which to form any verydecided opinion one way or the other. That the cantilever monoplane has a certain number of practical advantages may,perhaps, be granted, and if some new form of wing con- struction could be devised which would reduce the wingweight while still giving adequate stiffness and absence of flutter, there is little doubt that the monoplane would gainin popularity. Whether the Stieger wing system will solve the riddle yet remains to be seen. In the communicationsent to us by the Mono-spar Company, reference is made to comparative tests made on a section of a mono-spar wingand on a cantilever wing of more " orthodox " design. Both types of test wing were about one-third of the complete wing,and both were designed to the same factors, loading, area, etc. The weight of the original section was, the memorandumstates, 610 lbs., with an area of 254 sq. ft., and a wing loading of 17 -4 lb./sq. ft. The corresponding mono-spar test section•weighed 185 lbs., to which has to be added the actual fabric covering and certain parts which were irrevelant to the test,bringing the total weight of the mono-spar section up to 265 lbs. or less than 1-1 lbs./sq. ft., whereas the weight of the" "-4"1""''—" section was 2-4 Ibs./sq. ft. These figures composed of wires such as the leading edge wire (it can, ofcourse, be a metal strip or any other form capable of action as a tension member) the drag wires and the trailing edgewire. The drag bracing crosses over and under the spar, and is attached to top and bottom flange of spar at points ofintersection. It should be realised that in a wing of this type, muchdepends upon the " end fixings," i.e., the system is unstable, DRAG MEMBER TORSION AND DRAG BRACING FORMER RIBS MAIN RIBS •ANTI DRAG MEMBER orthodox as shown in the diagram, and requires for its completion someform of end attachment which will stabilise it. For instance, at the wing tip^ one may imagine two diagonal struts runningone from the nose of the outer rib to some point on the front of the spar farther inboard, and another from the rear portionof the rib to the back of the spar, opposite the joint of the front diagonal strut. At the root there will, it is supposed,be a similar arrangement, or the leading and trailing edge wires may be anchored to the fuselage, to which also would,in that case, be secured the innermost rib at the points where the drag bracing is attached. Otherwise the rib would, ,ofcourse, buckle laterally under the tension of the wires. These details are not shown in the diagram, as they were notsupplied to us, but attention should be called to the necessifcy for them. , Claims.—From the memorandum sent us by the Mono-sjiarCompany, we quote the following advantages claimed for the Stieger mono-spar wing system :— (1) Considerably lighter than any other cantilever wing.(2) Makes it possible to have the aerodynamic advantage? of a full cantilever wing with the lightness of the correspondingbiplane (3) All stresses can be accurately calculated. (4) Particular care has been taken to overcome " flutter/' (5) Torsional stiffness is unaffected by bending loads appliedto the wings. (6) The degree of torsional stiffness can tie accurately calculated, and if necessary can fie altered to suitchanged conditions. (7) For a given torsional strength, the stiffness is greater. (8) Great robustness of all members(9) Freedom from obstructions within the wing, making room for tanks, etc. (10) The well-tried fabric covering canare rather startling, but the data available are insufficient be employed. (11) The provision of three stiffly supported to form a basis for strict comparison. We learn that theactual test wing is to be exhibited at Olympia, as well as points within the wing structure - for attaching • engines, undercarriage, etc. (12) Cheapness of manufacture. : - :'• 476
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